This invention relates to apparatus for verifying the authenticity of documents, and more particularly, to such apparatus for detecting a metallized security thread embedded in currency paper.
It is known in the art of currency and banknote papers to incorporate a security thread. The use of such security threads has increased due to the prevalence of high-resolution, true-color photocopying machines. If modern currency or banknote papers do not have an embedded security thread, the currency can be more easily duplicated with a color photocopier. However, if the security thread is embedded within the paper, the characteristics of the thread are harder to illicitly reproduce.
The thread may comprise a plastic film having selected aluminum characters formed on a surface. The thread is embedded within the currency paper and is not present on either surface of the paper. Such security threads for use in U.S. currency are described in greater detail in U.S. Pats. Nos. 4,652,015 and 4,761,205 to Timothy Crane, both assigned to Crane & Co., Inc.
The security thread described in these patents has printed characters thereon of extreme fine-line clarity and high opacity such that human-readability of the printing is possible by means of transmitted light. Yet, the printing remains completely indiscernible under reflected light. If the printing were legible under reflected light, the public could rely upon the presence of the printed matter solely under this reflected light. The printing would then be easily replicated by counterfeit means. The aforementioned patents to Crane insure that the public does not come to rely on such an easily simulated security thread characteristic. This is accomplished by a method of manufacturing currency and banknote paper containing a security thread that is virtually invisible under reflected light with no manifestation on the surface of the currency or banknote that such a security thread is present within the note. Thus, authentification of such a security thread is carried out in a two-fold test; namely, wherein the thread is legible under transmitted light and invisible under reflected light.
An easy way of checking the authenticity of such a security thread is to place the currency under an intense light source to observe the characters of the thread by the human eye. However, in commercial situations where such an intense light source is unavailable, thus making a human check for thread presence and authenticity virtually impossible, it is desirable to provide means for automatically determining the thread's presence and authenticity. Various known means for providing verification of the presence and authenticity of the aforementioned security thread are exemplified in U.S. Pats. Nos. 4,980,569 and 5,151,607.
The '569 patent discloses a verification device comprising two optical light source/detector pairs disposed on opposite sides of a currency paper. The source and detector pairs are arranged for transmission and reception of optical energy through the currency if the thread is not present. Also, the source and detector pairs can determine the presence of a counterfeit thread on the currency surface by checking for light reflected off of the currency surface. Thus, the '569 patent provides a two-fold test wherein the thread, to be genuine, must be detected under transmitted light, and not be detected under reflected light. However, the device in the '569 patent may give a false indication of the authenticity of a counterfeit currency when a pencil line is drawn on the currency surface at the normal thread location.
In an attempt to overcome the shortcomings of the '569 patent, the '607 patent discloses a verification device comprising the optical means of the '569 patent in combination with a magnetic detector. The magnetic detector determines the presence of the security thread, while the optical means determines whether the thread is properly within the currency or improperly disposed on either surface.
In light of the shortcomings of optical methods of verifying the presence of the security thread within the currency paper, other means have been developed, such as capacitive verification devices. These devices operate on the principal of detecting a change in capacitance of a sensor, such change being due to the dielectric properties of the metallized security thread. The metallized security thread has dielectric properties that are vastly different from those of the paper in which it is embedded. The security thread operates as one plate of a capacitor, and draws charge off of a second plate of the capacitor, the second plate typically being a part of the verification device. Thus, the security thread effectively increases the capacitance that is sensed by the verification device, a detectable feature.
However, capacitance verification devices have shortcomings in that they can also be fooled by conductive marks, such as pencil lines, placed on the surface of the currency. This can be especially problematic for currency verification devices that are intended to be used for unattended transactions; for example, in vending machines that incorporate currency acceptors. Automatic vending machines, such as those that dispense soft drinks and cigarettes, are gradually accepting higher denomination currency bills in unattended transactions as payment for the goods. This is due to the inflationary prices of the goods. Also, unattended bill acceptors are expanding into areas such as gaming and other entertainment vending areas, and gas stations. The addition of bill acceptors and/or changers in these vending machines has resulted in a large increase in sales for unattended transactions. For these types of machines, it is imperative that the bill acceptor/changer have some means for reliably discriminating between genuine and counterfeit bills.
Accordingly, it is a primary object of the present invention to provide a capacitive-induction, security thread verification device that differentiates a counterfeit conductive line on a surface of currency paper from a genuine security thread embedded within the currency paper.
It is a general object of the present invention to provide a reliable security thread verification device for use in bill acceptors/changers in markets which require a high level of security in the verification device as these markets add increasingly high denomination capabilities into the acceptor/changer apparatus.
It is another object of the present invention to provide a device that verifies the presence of a genuine security thread embedded within currency paper by utilizing the known physical spacing between the metallized electrically-conductive characters formed on a surface of a non-conductive thread substrate embedded within the currency paper.
It is a still further object of the present invention to provide a capacitance-based, security thread verification device that is used for slower-speed, narrow-end-fed bill acceptor/changer devices that are incorporated into unattended, self-serve vending machines, bill changers, and the like.
It is a still further object of the present invention to machine-detect the presence of an advanced counterfeit deterrent thread in currency in a wide array of commercial, unattended cash-handling devices.
It is yet another object of the present invention to provide a counterfeit detection capability for currency paper that is superior to currently available technologies, such as optics and magnetics.
It is still another object of the present invention to reliably identify counterfeit currency regardless of the quality of the banknote or the counterfeit.
It is yet still another object of the present invention to provide a security thread verification device that is relatively inexpensive and easily incorporated into existing automated, unattended vending machines.
It is another object of the present invention to provide a security thread verification device with increased speed and reliability of counterfeit detection.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.